The present invention relates to the field of cathode ray tube manufacture, particularly frit knocking. More specifically, the present invention relates to a device and method for preventing arcing during an evaluation of the frit seal in a cathode ray tube using an external high-voltage probe. The present invention provides an insulating member placed on or adjacent to the high voltage probe tip, between the probe tip and the grounding band on the frit seal, that prevents arcing.
Cathode ray tubes (xe2x80x9cCRTsxe2x80x9d) are well known in modern society. The CRT is the principal component in such common devices as television sets and computer and video monitors. As shown in FIG. 1, a CRT (100) typically includes a relatively flat display portion (101) (upper portion as seen in FIG. 1). When one is watching television or looking at a computer monitor, that person is looking at the flat display portion (101) of a cathode ray tube. Below the display portion (101) is a funnel portion (102) that narrows into the xe2x80x9cneckxe2x80x9d of the CRT.
During manufacture, an electro-luminescent material such as phosphorus is coated over the display portion (101) of the CRT. The display portion (101) is then joined to the funnel (102) using a glass paste compound known as frit. A bead of frit is distributed around the interface between the funnel (102) and the display portion (101). The frit is the then cured or hardened to form an airtight seal between the display portion (101) and the funnel (102). This seal may be referred to as a frit seal (103).
An electron gun (not shown) is then placed at the end of the CRT""s xe2x80x9cneckxe2x80x9d (102). When the CRT is operated, a yoke (not shown) creates an electromagnetic field and causes the stream of electrons emitted from the electron gun to scan in lines across the surface of the display portion (101). Where the stream of electrons hits the electro-luminescent material, the electro-luminescent material emits light. Thus, by rapidly switching the electron stream on and off, or by varying the power of the electron stream as it sweeps across the display portion of the CRT, an image can be formed in the light emitted by the electro-luminescent material. This is the general principle on which CRTs operate.
After the display portion (101) of the tube is joined to the funnel (102) and the joint between the two is sealed with frit, the completed tube is evacuated. Then, the strength of the frit seal (103) and the integrity of the vacuum are evaluated. This evaluation is known as xe2x80x9cfrit knockingxe2x80x9d and is performed by applying a high-voltage to the anode or funnel portion (102) of the CRT.
In the frit knocking process, a conductive band or strap (104) is wrapped around the frit seal (103) and is in physical and electrical contact with the frit seal (103). The conductive band (104) is grounded (105) as shown in FIG. 1. A high-voltage probe (106) is then positioned to apply a voltage to the anode of the CRT. The probe (106) is connected to a voltage source (109) that provides a high voltage output. The tip (107) of the probe is then brought into contact with a point (108) on the anode or funnel portion (102) of the CRT (100).
If there is any flaw in the frit seal (103), such as an opening, a fracture, a gap, etc., the high-voltage probe (106) will create an electrical arc from within the CRT (100), through the flaw in the frit seal (103) and into the grounded band (104). If such arcing is detected, the failure or lack of integrity in the frit seal (103) is also detected. If such arcing is detected, the CRT (100) must be removed from the production line so that the frit seal (103) can be repaired, patched or replaced. Otherwise, the flaw in the existing frit seal may degrade or even disable the performance of the CRT (100).
While this method provides an adequate means of testing or xe2x80x9cknockingxe2x80x9d the frit seal in a cathode ray tube, there are also significant problems. Specifically, the distance (d) between the tip (107) of the high-voltage probe (106) and the grounded band (104) is small enough that electrical arcing (130) may occur outside the CRT (100) between the probe tip (107) and the grounded band (104).
This arcing (130) poses many problems. For example, the arcing (130) may be detected and attributed to a flaw in the frit seal (103). If this error is not detected, the CRT (100) will not pass the evaluation even though its frit seal (103) may be in perfect condition. Additionally, even if the error is detected, time may be required to reset the testing apparatus that is erroneously registering a flaw in the frit seal (103). External arcing (130) may also damage the equipment being used to evaluate the frit seal (103).
Consequently, in order to more effectively and efficiently test a frit seal (103), the art requires some new means and method of frit knocking that prevents such external arcing between the probe and grounded band
The present invention meets the above-described needs and others. Specifically, the present invention provides a novel device and method that prevents electrical arcing external to a cathode ray tube that may otherwise occur between a high-voltage probe and a grounded band on the frit seal of the cathode ray tube during testing or xe2x80x9cknockingxe2x80x9d of the frit seal.
Additional advantages and novel features of the invention will be set forth in the description which follows or may be learned by those skilled in the art through reading these materials or practicing the invention. The advantages of the invention may be achieved through the means recited in the attached claims.
The present invention may be embodied and described as a method of preventing arcing external to a cathode ray tube and between a high-voltage probe and a grounded band disposed around the exterior of a frit seal of the cathode ray tube during evaluation of the frit seal. The method is performed by disposing an insulating member between the high-voltage probe and the grounded band. The insulating member prevents the arcing external to the cathode ray tube between the high-voltage probe and the grounded band.
The method of the present invention may include forming the insulating member as a solid piece of insulating material. Alternatively, in a preferred embodiment, the method is performed by forming the insulating member from a skin of flexible insulating material filled with a second insulating material. The skin on the insulating member may be formed of rubber. The second insulating material is preferably a non-conductive gel.
The method of the present invention may also include forming the insulating member in an oval or spherical shape. Alternatively, the insulating member may be formed with an annular shape. If an annular shape is used, the insulating member may be disposed between the high-voltage probe and the grounded band by extending a tip of the high-voltage probe through the center opening in the annular insulating member.
Preferably, the method of the present invention also includes deforming the flexible skin around a portion of the high-voltage probe and a portion of the cathode ray tube. This helps insure that the insulating member with will prevent, or at least minimize, any arcing external to the cathode ray tube between the high-voltage probe and the ground band on the frit seal.
Finally, the method of the present invention may include applying a voltage to the anode of the cathode ray tube with the high-voltage probe; detecting electrical arcing through the frit seal and into the grounded band; and, if electrical arcing is detected, removing the cathode ray tube from the production line for repair of the frit seal.
The present invention also encompasses the insulating member itself, as well as the methods of making and using the insulating member described above. Stated more specifically, the present invention encompasses an insulating member for preventing arcing external to a cathode ray tube and between a high-voltage probe and a grounded band disposed around the exterior of the frit seal of the cathode ray tube during evaluation of the frit seal of the cathode ray tube. In this case, the insulating member is sized and shaped so as to electrically insulate against the external arcing. The insulating member is also sized and shaped so as to be disposed between the high-voltage probe and the grounded band during the evaluation of the frit seal such that the insulating member prevents the arcing external to the cathode ray tube between the high-voltage probe and the grounded band.
As before, the insulating member may be a solid piece of insulating material or may be a skin of flexible insulating material filled with a second insulating material. In such a case, the skin is preferably formed of rubber and the second insulating material is preferably a non-conductive gel.
The insulating member may have an oval or spherical shape. Alternatively, the insulating member may have an annular shape. If the annular shape is used, the central opening of the annulus is sized and shaped to receive the tip of the high-voltage probe, which extends through the opening when the insulating member is disposed on the probe.